In the development of advanced press-fit prosthesis stems, such as hip stems, accurate preparation of the bone canal is extremely important in order to guarantee good cortical contact with and load transfer from the stem to the bone. Examples of prior art press-fit prosthetic hip stems may be had in the Dow Corning Wright publication "McCutchen Hip System" bearing copyright date 1988 and identification number 235-1187T. Some existing prosthesis stems are designed with a conical proximal region to distribute the load and an anti-rotation lug to fix and maintain the accurate position of the joint portion of the prosthesis.
Bone canals for these prosthesis stems are presently prepared by drilling the resected distal end of the bone and then reaming the drilled hole to provide a frustoconical seat for the trochanteral portion of the prosthesis stem. The bone canal is then cut at an angle with a milling cutter to provide a slanted groove for seating the anti-rotation lug by dead-reckoning, i.e., by the surgeon eyeballing the appropriate location of the tool axis and angle in a procedure that often does not result in accurate seating of the anti-rotation lug. Alternatively, the bone canal can be prepared as taught in U.S. Pat. No. 5,135,529 to Paxson et al, issued Aug. 4, 1992 and assigned to the assignee of the subject invention, the disclosure of which is hereby incorporated by reference and relied upon. In Paxson et al, modular unitary rasp blocks of varying sizes are used to form the slanted groove to receive the anti-rotation lug. Again, the procedure often does not result in accurate seating of the anti-rotation lug.
The primary disadvantage of the prior art bone canal preparation techniques is that accurate and predictable results are difficult to obtain. Additionally, the prior art medical instruments used to prepare the bone canal for prosthesis implantation are often cumbersome and somewhat difficult for a single surgeon to operate, and often do not readily adapt themselves for accommodating various prosthesis stem configurations.